Research

In the last two decades diabetes in adolescents has been reported with increasing frequency (SEARCH, 2007). Additionally, adolescent’s exposure to harmful levels of sound has become more common. In particular, the rise in use of portable music players may impose risk for adolescents not aware of the insidious risks of hearing loss imposed by the mixture of elevated sound intensity and prolonged exposure duration (Zogby, 2006). Recent animal studies indicate increased risk in diabetics for hearing loss related to noise and age (e.g., Wu et al., 2009). The combination of increased noise exposure and increased risk of hearing loss may have profound implications for the hearing of diabetics, particularly young diabetics with high levels of noise exposure. Despite this evidence no study has examined the relationship between noise exposure and hearing loss in a human diabetic population. The broad long-term goal of the proposed research is to study the association of diabetes with susceptibility to noise-related hearing loss. The goal of this pilot study is to assess the relationship between diabetes, noise, and hearing loss in a sample population of adolescents/young adults with type 1 diabetes. Three specific aims will (1) characterize auditory function using methods sensitive to subtle changes in cochlear and neural function; (2) determine noise exposure via questionnaire/activity cards and personal dosimeter measures to estimate noise-dose risk for auditory damage; and (3) explore associations between diabetic control and measures of hearing, cochlear function, auditory neural integrity, and susceptibility to noise related hearing loss. These aims will be accomplished through evaluation of 50 experimental subjects aged 12-22 years diagnosed with type 1 diabetes and 50 matched control subjects. New techniques that are uniquely sensitive to subtle changes in auditory cochlear and neural function will be used. The determination of factors associated with hearing loss in diabetics has direct implications on reducing susceptibility and severity of hearing loss in the diabetic population. In addition, this study will provide an examination of the ability of the most sensitive outcomes measures available to detect damage in an etiology representative of compromised auditory metabolic function.

Evidence from animal models suggests that oxidative stress and vascular integrity are important in the pathogenesis of sensorineural hearing loss (SNHL) and that dietary nutrients that have roles in these processes may influence susceptibility to SNHL. The purpose of this study was to examine associations between total nutrient intakes and auditory function outcomes in an older human population. Descriptive characteristics and dietary data from food frequency questionnaires were collected from 2111 Australians aged 49-99 years in a cross-sectional study design and analyzed for associations with auditory function outcomes (ie, otoacoustic emissions and pure tone averages measured in a sound-treated room by a trained audiologist). Increased carbohydrate, vitamin C, vitamin E, riboflavin, magnesium and lycopene intakes were significantly associated with better auditory function. Increased cholesterol, fat and retinol intakes were significantly associated with poorer auditory function. These data demonstrate that nutrients that function in oxidative homeostasis and vascular integrity are associated with auditory function. The findings indicate that further investigation is warranted to determine which nutrients are predictive of SNHL in humans as well as how combinations of nutrients interact with auditory function.

Rodents have proven to be a useful model system to screen genes, ototoxic compounds and sound exposure protocols that may play a role in hearing loss. High-throughput screening depends upon a rapid and reliable functional assay for hearing loss. This study describes the use of a frequency modulated (FM) chirp stimulus as an alternative to the click to derive a rapid assessment of auditory brainstem response (ABR) threshold in the rodent. We designed a rising frequency A-chirp based upon the spatial mapping of preferred frequency along the rat basilar membrane to provide a more synchronous and equipotent input across the length of the cochlea. We observed that the ABR wave I and wave IV amplitudes evoked by the A-chirp were significantly greater than the click and that A-chirp minimum response thresholds were lower than the click. Subsequent analyzes compared the efficacy of the A-chirp to linear, time-reversed and amplitude-reversed chirps and confirmed that the A-chirp was most effective chirp configuration. These data suggest that the A-chirp may be optimally suited as a single screening broad frequency stimulus for rapid ABR threshold estimations in the rodent and could serve to complement more detailed frequency-specific physiologic and behavioral estimates of hearing threshold.

31. Hood LJ, Wilensky D, Li L, Berlin CI. 2004. The role of FM technology in the management of patients with auditory neuropathy/dys-synchrony. Proceedings of the International Conference on FM Technology, Chicago, Illinois.

32. Rose K, Hood LJ, Berlin CI. 2001. An overview of the evolution of auditory neuropathy – Its diagnosis and management. ASHA Special Interest Group Publication.